In wireless communication systems, mobile stations (MSs) may exchange signals with one or more base station terminal systems (BTSs) which can provide service within a surrounding geographic region. A coordinated network of BTSs may provide wireless communication service to an expansive coverage area. However, due to various geographic, electromagnetic and/or economic constraints, the network of BTSs may lack adequate communication services in some areas within a desired coverage area. These “gaps” or “holes” in the coverage area may be filled with the use of repeaters.
Generally, a repeater is a high gain bi-directional amplifier. Repeaters can receive, amplify and re-transmit signals in both the uplink direction (from the MS to the BTS) and the downlink direction (from the BTS to the MS). The repeater may provide communication service to the coverage hole, which was previously not serviced by the BTS. Repeaters may also augment the coverage area of a sector by shifting the location of the coverage area or altering the shape of the coverage area. Conventional repeaters may utilize fixed gains which may not be optimal as the MS changes location and/or as the channel conditions vary. Moreover, in communications systems where controlling power is important to good system performance (e.g., CDMA systems), each MS within a cell may have its power settings under direct control of the serving BTS. Conventional repeaters having a fixed repeater gain may not be amenable to these standard types of BTS power control.
In addition, a repeater is not a noiseless device and may contribute additional noise into the receiver at the BTS. While one repeater may not appreciably increase the noise floor at the BTS, the cumulative effect of many repeaters may noticeably raise the noise floor of the BTS, thereby reducing the effectiveness of the communication links in the coverage area. While the amount of signal and noise broadcast back to the BTS can be manipulated by adjusting the repeater gain and the repeater to donor antenna gains, it may be challenging to simply set the total link gain to a desired value in conventional repeaters.
Moreover, some repeaters may perform various signal processing operations in the digital domain (e.g., interference cancellation repeaters designed to reduce feedback between uplink and downlink channels). Accordingly, these repeaters will use analog-to-digital converters (ADCs) which typically require the dynamic range of the analog signal input to be within a designated range, depending upon the number of bits output by the ADC. If the input analog signal exceeds the dynamic range of the ADC, non-linear forms of noise may result. For example, if the input analog signal is too low, quantization noise may become dominant and significantly degrade the digital conversion process. At the other extreme, if the input analog signal level is too high, the ADC will become saturated, and the full scale value of the ADC's output will be exceeded.
Conventional approaches to avoid these types of non-linear distortion typically involve automatic gain controllers (AGCs) to limit the dynamic range of the analog signal so that it “fits” into the ADC. However, for interference cancellation repeaters, the AGC prevents accurately estimating the feedback channel because step changes in signal amplitudes can cause oscillations. Accordingly, for interference cancellation repeaters, the ADCs conventionally utilize a wider dynamic range (i.e., a large number of bits) in order to properly accommodate the wide range in levels of the input signals, which include both the communication signals and the feedback signals appearing at the front end of the repeater. Utilizing ADCs capable of accepting such wide dynamic ranges increases costs, both for the ADC components themselves, and for subsequent digital components having to accommodate more bits being provided by the ADCs.
Accordingly, it may be desirable to adjust the gain within the repeaters using simple and cost effective techniques in order to reduce the noise floor seen at the receiver of the BTS, and to reduce costs of the ADCs and associated digital components in digital signal processing repeaters.